This invention relates to a cemented carbide and a cutting tool using a cemented carbide, and more particularly to a cemented carbide and a cutting tool having a hardness and a toughness suitable for cutting of a hardly machinable material such as a stainless steel, besides a steel and cast iron, such as a carbon steel and an alloy steel, and further excelled in a wear resistance.
As a cemented carbide widely used for cutting of metal, a WC Co alloy which is composed of a hard phase wherein tungsten carbide WC is a main component, and a binder phase of iron-group metals, such as cobalt), or an alloy wherein a carbide, a nitride, a carbonitride, etc. of metals of groups 4a, 5a, or 6a in the periodic-table were further added to the WC-Co is known.
Generally, as a method of manufacturing this cemented carbide, a method comprising the steps of: grinding, mixing and molding a raw material powder which constitutes the above cemented carbide, and sintering at 1350-1600xc2x0 C. for about 1 to 3 hours, is known.
These cemented carbide is mainly applied to cutting of a cast iron, a carbon steel, etc. as a cutting tool. Recently, as for a cemented carbide, application to cutting of a hardly machinable material represented by stainless steel is also considered.
However, since such a cutting difficult material has characters such as generation of work hardening, high affinity with tool material and low thermal conductivity, many problems has generated in the field of cutting. That is, a cemented carbide which has toughness and hardness is needed for processing of a stainless steel.
When cutting of the hardly machinable material, such as a stainless steel, is carried out with a cutting tool made from K-grade cemented carbide which is composed of WC-Co system cemented carbide specified to JIS B 4053 (1996) which is comparatively few amounts of Co, or a cutting tool made from P-grade cemented carbide which has B1 type (cubic type) solid solution of single composition, wear or a cutting tool progresses rapidly, or a fracture whose welding is considered to be a cause is generated, a processing surface state of cutting material gets worse. As a result, it becomes a tool life for a short time, and good cutting can not be performed.
Moreover, a damage to primary notch parts with a cutting force received from a processing surface which carried out work hardening is intense, and it results in a tool life immediately, and comes to acquire good cutting characteristics.
Furthermore, a conventional cemented carbide contains an iron (Fe) and a chromium (Cr) as an impurity. When such a cemented carbide is used as a cutting tool, Fe and Cr combine with a large amount of an iron (Fe) and chromium (Cr) which are contained in a workpiece of which a temperature was raised during cutting. As a result, welding or agglutination of the workpiece to the cutting tool surface is carried out, and action parts (piece edge etc.) are unusually worn out, or a cutting force is increased, whereby it becomes easy to generate damage on a cutting tool surface.
Moreover, there was a problem that a finished-surface coarseness of a surface to be cut deteriorates by an unevenness of a welding thing or an agglutination thing.
An iron (Fe) and a chromium (Cr) in are contained in a primary raw material as an unescapable impurity, or are contained in the cemented carbide during a manufacturing process, and cannot be perfectly removed on industry. Moreover, a content of iron (Fe) and chromium (Cr) which are contained during a manufacturing process is uncontrollable, since it is changeable in connection with change or process and surface states of a grinder or the like.
Moreover, since iron has high affinity with carbon, if a content of iron (Fe) in a surface of the cemented carbide is large, carbon and iron (Fe) combine preferentially, in coating a hard coat by vapor phase synthetic methods, such as CVD and PVD. Accordingly, it become easy to generate embrittlement phases, such as xcex7 phase, to an interface of the cemented carbide and the hard coat, and an adherence strength or a hard coat falls. Consequently, the hard coat is exfoliated and destroyed, or a life falls in using as cutting tool or slide member.
In order to improve a wear resistance, a method of coating a hard coating of higher hardness on an alloy surface is known. In order to relax an impact to the hard coating, the method of forming the so-called xcex2-free layer wherein a content of B-1 type solid solution is reduced, to a surface area to which a hard coating of the cemented carbide is formed is known.
Furthermore, Japanese Unexamined Patent Publication No. 6-93473 discloses that a content of Zr existing in a depth region of 1-50 xcexcm from a base material surface to insides is disappeared or decreased, when using Ti and Zr as a B-1 type solid solution (without using Nb).
However, it is known that when surfaces of these cemented carbides are oxidized and deteriorated with a heat at the time of cutting and oxygen in environment, its hardness and toughness fall. For this reason, even when a hard coating is coated on an alloy surface, an alloy surface may be exposed to an oxidizing atmosphere by existence of a defective portion in a hard coating. Especially, if a xcex2-free layer is formed in an alloy surface (that is, p1suf/pin less than 0.9, and q1suf/qin less than 0.9, each sign of which is defined as an after-mentioned), it will be easy to generate oxidization and deterioration of an alloy surface.
On the other hand, when not forming a xcex2-free layer directly under a hard coating (p1sufxe2x88x92p2suf=pin, q1suf=q2suf=qin, each sign of which is defined as an after-mentioned), the shock resistance and fracture resistance of the hard coating will fall.
Furthermore, like a coating cemented carbide disclosed in Japanese Unexamined Patent Publication No. 6-93473, when there are few contents of Zr in a surface region of a base material (q1suf/qin less than 0.9, each sign of which is defined as an after-mentioned), plastic deformation resistance worsens and wear resistance falls.
A main object of this invention is to provide a cemented carbide which has high hardness and a toughness.
Other object of this invention is to provide a cemented carbide that welding and adhesion with workpiece in the time of cutting and sliding etc. can be inhibited, and a good hard coat layer can also be formed.
Other object of this invention is to provide a surface coating cemented carbide which is excellent in oxidation resistance while having high hardness and high toughness, and can improve high fracture resistance and high wear resistance in severe environment as exposed to high temperature by continuation operation etc.
Another object of this invention is to provide a cutting tool which shows excellent wear resistance, plastic deformation resistance, and fracture resistance in case of cutting of a hardly machinable material, such as stainless steel.
(1st Cemented Carbide)
Inventors found out the new fact that when providing, in cemented carbide, the surface region of 90-98% of the minimum hardness as compared with the hardness in an inside, a cemented carbide, which has hardness sufficient to processing of a hardly machinable material, and which has toughness being capable of bearing the impact starting in the time of cutting the surface from which work hardening was started, was obtained.
Moreover, inventors found out that the new fact that, when (1) two or more B1 type solid solution phases exist in cemented carbide, (2) at least one this B1 type solid solution phase is B1 type solid solution phase with high contents of Zr, as compared with other B1 type solid solution phases; and (3) existence states differs in the inside near the surface of the cemented carbide, the above-mentioned effects are acquired characteristic.
That is, the 1st cemented carbide of this invention is composed of a hard phase component which comprises a tungsten carbide WC and at least one selected from carbides, nitrides and carbonitrides of metals of the groups 4a, 5a and 6a in the Periodic Table; and a binder phase component comprising at least one iron-group metals, wherein the surface region of this cemented carbide has 90-98% of the minimum hardness as compared with internal hardness.
The 1st cemented carbide of this invention contains Zr as a metal selected from the groups 4a, 5a and 6a in the Periodic Table. The ratio of Zr in metals of the groups 4a, 5a and 6a in the Periodic Table has a high region near the surface as compared with the inside of the cemented carbide. Further, the thickness of the area wherein the content ratio of Zr is high as compared with the inside of the cemented carbide may be 5 to 100 xcexcm.
Two or more B1 type solid solution phases may exist in the cemented carbide, and one of them is B1 type solid solution phase with high contents of Zr as comparing with other B1 type solid solution phases.
The mean particle diameter of B1 type solid solution phase with high contents of Zr may be 3 xcexcm or less.
When the content of Ta among metals of the groups 4a, 5a and 6a in the Periodic Table is 1% by weight or less in TaC conversion in the whole quantity, the cemented carbide having good tool characteristics is obtained.
The 1st cutting tool of this invention is composed of the 1st cemented carbide mentioned above, or is composed of the 1st cemented carbide and a coating, as mentioned later, on the surface of the 1st cemented carbide.
A coating may be composed of at least one selected from metal carbide, metal nitride, metal carbonitride, TiAlN, TiZrN, TiCrN, a diamond and Al2O3. The above-mentioned metal is selected from the groups 4a, 5a and 6a in the Periodic Table. The coating is a single layer or two or more layers.
(2nd Cemented Carbide)
Inventors found out the following facts. That is, in a cemented carbide containing a WC phase and a binder phase of a iron-group metal, at least two solid solution phases selected from carbides, nitrides, and carbonitrides of metals of the groups 4a, 5a and 6a in the Periodic Table and containing Zr and Nb at least, are precipitated. Further, the cemented carbide has the 1st phase having a peak in 2xcex8=40.00-41.99xc2x0 and the 2nd phase having a peak in 2xcex8=38.00-39.99xc2x0 in the X-ray diffraction of the cemented carbide. As a result, hardness and high temperature strength of the cemented carbide can be raised.
A cutting tool obtained by using the cemented carbide of this invention has wear resistance, plastic deformation resistance, and fracture resistance which were excellent in cutting of hardly machinable material, such as stainless steel, and high efficiency cutting is attained.
That is, the 2nd cemented carbide of this invention comprises a WC phase, at least two solid solution selected from carbides, nitrides and carbonitrides of metals of the groups 4a, 5a and 6a in the Periodic Table and containing Zr and Nb at least, and a binder phase containing at least one iron-group metal, wherein the cemented carbide has the 1st phase having a peak in 2xcex8=40.00-41.99xc2x0 and the 2nd phase having a peak in 2xcex8=38.00-39.99xc2x0 in the X-ray diffraction of the cemented carbide.
Here, it is desirable that the ratio (p2/p1) of strength (p1) of the 1st peak, and strength (p2) of the 2nd peak is 0.1-2. The content ratio (Zr/Zr+Nb) of Zr and Nb may be 0.5-0.7. The cemented carbide having the surface region of p2 greater than 0 and p1=0 shows toughness and the excellent fracture resistance.
Even when a Ta content is 1% by weight or less in TaC conversion in the whole quantity of the metals of the 4a, 5a and 6a groups of the Periodic Table, the cemented carbide which has excellent tool characteristics is obtained.
Furthermore, it is desirable to contain the WC phase at the ratio of 60-95 volume %, and to contain the binder phase at the ratio of 1-20 volume %.
Moreover, as for the cutting tool which consists of the above cemented carbide, it is especially desirable to comprise such cemented carbide and at least one coating selected from the group consisting of metal carbide, metal nitride, metal carbonitride, TiAlN, TiZrN, TiCrN, diamond and Al2O3 and provided on the surface of the cemented carbide. The above-mentioned metal is selected from the 4a, 5a and 6a groups of the Periodic Table. The coating is a single layer or two or more layers.
(3rd Cemented Carbide)
Inventors found out the facts that in order to inhibit the influence of iron (Fe) and chromium (Cr) to workpiece, it is effective to control the content of iron (Fe) and chromium (Cr) in cemented carbide, and to reduce the content ratio of iron (Fe) and chromium (Cr) to the cobalt (Co) and/or nickel (NI) in the surface of the cemented carbide than that in the inside of the cemented carbide. Accordingly, welding and adhesion with workpiece can be inhibited, and in case that a hard coat is formed, the cemented carbide coated with a good hard coat is obtained
That is, the 3rd cemented carbide of this invention comprise 2 to 20% by weight of a binder metal comprising cobalt (Co) and/or nickel (nickel), 0 to 30% by weight of at least one selected from carbides, nitrides and carbonitrides of metals of the groups 4a, 5a and 6a in the Periodic Table, 10 to 300 ppm of iron (Fe), 100xcx9c1000 ppm of chromium and tungsten carbide and unescapable impurities as remainder, wherein a surface region satisfies the conditions of psuf less than pin, wherein psuf and pin are defined below.
pin.=w2 in/w1 in 
psuf=w2 suf/w1suf 
w1in: a content of the binder metal inside the cemented carbide
w2in: a content of Fe and Cr inside the cemented carbide
w2suf: a content of the binder metal in the surface region of the cemented carbide
w1suf: a content of Fe and Cr in the surface region of the cemented carbide
The maximums of the ratio (pout/pin) of psuf and pin in the surface region may be 0.5 to 0.95. The thickness of the surface region may be 1 to 20 xcexcm.
It is desirable to cover with the total thickness or 1-30 xcexcm at least one layer of the hard coats which consist of at least one selected from metal carbide, metal nitride, metal carbonitride, TiAlN, TiZrN, TiCrN, DLC (diamond-like carbon), diamond and Al2O3 on the surface of cemented carbide. The above-mentioned metal is selected from the 4a, 5a, and 6a groups in the Periodic Table.
The method of manufacturing the 3rd cemented carbide is composed of steps of:
grinding and mixing the raw materials powder comprising of tungsten carbide powder, at least one powder selected from carbides, nitrides and carbonitrides of metals of the 4a, 5a, and 6a group in the periodic-table, and at least one material of cobalt (Co) and nickel (Ni),
molding the resulting mixture,
retaining a green body obtained for 0.3 to 2 hours at the 1st sintering temperature of 1350 to 1600xc2x0 C. in a non-oxidizing atmosphere,
cooling to the 2nd sintering temperature lower 20 to 200xc2x0 C. than the 1st sintering temperature, and
retaining at the 2nd sintering temperature in a vacuum for 1 to 3 hours.
It is desirable for portions in contact with raw material powders of a container and a grinding member used in the method of manufacturing the cemented carbide in case the raw material powders are ground and mixed not containing Fe and Cr.
(4th Cemented Carbide)
Inventors found out the facts that, when a 1st surface region and a 2nd surface region provided inside of the 1st surface region as mentioned below are provided to the surface of a cemented carbide, oxidation resistance of the cemented carbide forming a coating can be raised, in addition to raising toughness of the surface of the cemented carbide and raising fracture resistance of a hard coating. Accordingly, in case of operating continuously or intermittently for a long time, thereby exposing to high temperature for a long time, a surface coating cemented carbide has excellent fracture resistance and wear resistance.
(1) 1st surface region wherein the content ration of Zr is nearly equal to that of inside, and the content ratio of metallic elements M which is at least one selected from metals of the groups 4a, 5a and 6a in the periodic table, except for Zr, is low as compared with inside.
(2) 2nd surface region wherein the content ratio of Zr is nearly equal to that of inside, and content ratio of metallic elements M which is at least one selected from metals of the groups 4a, 5a and 6a in the periodic-table, except for Zr, is low as compared with inside.
That is, a surface coated cemented carbide of this invention is composed of a cemented carbide which comprises WC, at least one carbide, nitride and carbonitride of metallic element M which selects from metals of the group 4a, 5a and 6a in the periodic-table, and a binder material of iron-group metal, wherein metallic element M contains Zr and Nb, and the 1st surface region and the 2nd surface region which satisfy the relation shown below are provided within a region of depth of 5 to 200 xcexcm from the surface.
0.1xe2x89xa6q1suf/qinxe2x89xa60.9 
0.9xe2x89xa6r1 suf/rinxe2x89xa61.1 
1.1xe2x89xa6q2 suf/qinxe2x89xa61.5 
0.9xe2x89xa6r2 suf/rinxe2x89xa61.1 
qin=Min/Tin 
q1suf32 M1suf/T1suf 
q2suf=M2suf/T2suf 
rin=Zrin/Tin 
r1suf=Zr1 suf/T1suf 
r2suf=Zr2 suf/T2suf 
Min: Content ratio of metallic element M in the inside of the cemented carbide
Zrin: Content ratio of Zr in the inside of the cemented carbide
Tin: Content ratio of W in the inside of the cemented carbide
M1suf: Content ratio of metallic element M in the 1st surface region of the cemented carbide
Zr1suf: Conyent ratio of Zr in the 1st surface region of the cemented carbide
T1suf: Content ratio of W in the 1st surface region of the cemented carbide
M2suf: Content ratio of metallic element M in the 2nd surface region of the cemented carbide
Zr2suf: Content ratio of Zr in the 2nd surface region of the cemented carbide
T2suf: Content ratio of W in the 2nd surface region of the cemented carbide
It is desirable that the oxidation resistance of the surface coating cemented carbide is 0.01 mg/mm2 or less.
It is desirable that metallic element M satisfies the following relation in the whole cemented carbide.
0.1xe2x89xa6Zr/(Ti+Zr+Hf)xe2x89xa60.5, 
0.6xe2x89xa6Nb/(V+Nb+Ta)xe2x89xa61.0, and 
0.05xe2x89xa6Zr/(Zr+Nb)xe2x89xa60.8. 
Furthermore, it is desirable that the cemented carbide contains 0.1 to 1.5% by weight of ZrC, 0.5 to 3.5% by weight of NbC, 1.0 to 2.5% by weight of TiC, 0 to 1.0% by weight of TaC, 0 to 1.0% by weight of HfC, 0 to 1.0% by weight of Cr3C2, 0 to 1.0% by weight of VC, and 5 to 10% by weight of Co, and the residue consists of WC and unescapable impurities.
The thickness d2 of the 1st surface region may be 1-50 xcexcm, and the thickness d2 of the 2nd surface region may be 10-200 xcexcm.
Furthermore, the hard coating may be at least one layers selected from metal carbide, metal nitride, metal oxide, metal carbonitride, metal carbonation thing, metal nitride oxide, metal carbonated-nitride, and diamond. It is suitable that the above metal is selected from metals or the group 4a, 5a and 6a metal in the periodic-table, or aluminum.